JP6318790B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread used for a studless tire, which is excellent in performance on ice and wet performance.

  The rubber composition forming the tread portion of the studless tire is required to achieve both on-ice performance and wet performance at a high level. In order to improve the performance on ice, it is necessary to ensure flexibility in a low temperature state. Therefore, the glass transition temperature (Tg) of the base rubber is often designed to be low. However, when the Tg of the base rubber is lowered, the tan δ at 0 ° C. becomes small, and it becomes difficult to ensure wet performance.

  In order to increase the wet performance, for example, by blending a resin having a high softening point such as an aromatic modified terpene resin, the wet performance (tan δ at 0 ° C.) is not deteriorated without deteriorating the rolling resistance (tan δ at 60 ° C.). ) Is known to improve. However, if a resin with a high softening point is blended with the rubber composition for a tread of a studless tire as described above, the rubber hardness at low temperatures increases, and the flexibility and adhesion of the rubber are impaired, resulting in a decrease in performance on ice. Resulting in. For this reason, the on-ice performance and the wet performance need to have contradictory characteristics, and it has been difficult to improve both at a high level.

  On the other hand, Patent Document 1 proposes a rubber composition containing a crosslinkable oligomer or polymer that is incompatible with a diene rubber and three-dimensionally crosslinked fine particles having an average particle diameter of 1 to 200 μm in order to improve performance on ice. ing. However, the crosslinkable oligomer / polymer and three-dimensionally crosslinked fine particles incompatible with the diene rubber do not contribute to the improvement of the wet performance, and the wet performance is rather deteriorated depending on the Tg of the crosslinkable oligomer / polymer. There is a risk of it.

  Therefore, a technology for improving both the on-ice performance and the wet performance of the statless tire has not yet been established.

Japanese Patent No. 5229431

  An object of the present invention is to provide a rubber composition for a tire tread for use in a studless tire, wherein the performance on ice and the wet performance are improved to the conventional level or more.

  The rubber composition for a tire tread of the present invention that achieves the above object is a rubber composition comprising 100 parts by weight of a diene rubber, 20 parts by weight or more of silica, and 1 to 10 parts by weight of a liquid resin at room temperature. The diene rubber contains natural rubber and butadiene rubber, the average glass transition temperature is −60 ° C. or lower, the liquid resin at room temperature is an adduct of camphene and a phenol compound, and the glass transition temperature is It is -10 degreeC-10 degreeC, It is characterized by the above-mentioned.

  The rubber composition for a tire tread of the present invention comprises a diene rubber containing natural rubber and butadiene rubber and having an average glass transition temperature of −60 ° C. or less, and an adduct of camphene and a phenol compound, and has a glass transition temperature of −10. Since liquid resin is compounded at room temperature of 10 ° C to 10 ° C, tan δ at 0 ° C can be improved while keeping the rubber hardness soft at low temperature, thereby balancing the performance on ice and the wet performance. Can be improved beyond the conventional level.

  Also, 100 to 100 parts by weight of the diene rubber contains 0.3 to 30 parts by weight of a crosslinkable oligomer or polymer and 0.1 to 12 parts by weight of three-dimensionally crosslinked fine particles having an average particle diameter of 0.5 to 50 μm. Preferably, the crosslinkable oligomer or polymer is incompatible with the diene rubber and has a glass transition temperature of −50 ° C. or lower. Thereby, the performance on ice can be made more excellent while maintaining the excellent wet performance.

  Furthermore, it is preferable that 0.2 to 30 parts by weight of thermally expandable microcapsules is blended with 100 parts by weight of the diene rubber. As a result, the performance on ice can be further enhanced.

  The pneumatic tire using the rubber composition for a tire tread of the present invention in the tread portion has excellent performance as a studless tire, and can particularly improve on-ice performance and wet performance.

  In the present invention, the diene rubber used includes natural rubber and butadiene rubber, and contains these as main components. Here, the main component means that the total amount of natural rubber and butadiene rubber is 50% by weight or more with respect to 100% by weight of the diene rubber. By using these as main components, the performance on ice and snow of the rubber composition can be enhanced. The total of natural rubber and butadiene rubber is preferably 50 to 100% by weight, more preferably 70 to 100% by weight.

  In the present invention, diene rubbers other than natural rubber and butadiene rubber can be blended. Examples of other diene rubbers include isoprene rubber, various styrene butadiene rubbers, butyl rubber, and ethylene-propylene-diene rubber. Of these, styrene butadiene rubber is preferred. The content of the other diene rubber is preferably 0 to 50% by weight and more preferably 0 to 30% by weight in 100% by weight of the diene rubber.

  In the present invention, the average glass transition temperature of the diene rubber composed of natural rubber and butadiene rubber is −60 ° C. or lower, preferably −90 ° C. to −60 ° C. The average glass transition temperature of the diene rubber is -60 ° C or lower, maintaining the flexibility and flexibility of the rubber compound at low temperatures and increasing the adhesion to the ice surface. Can be. The glass transition temperature (Tg) of the diene rubber is measured by a differential scanning calorimetry (DSC) under a heating rate condition of 20 ° C./min, and is set as the temperature at the midpoint of the transition region. When the diene rubber is an oil-extended product, the glass transition temperature of the diene rubber in a state not containing an oil-extended component (oil) is used. The average glass transition temperature is the sum of the glass transition temperature of each diene rubber multiplied by the weight fraction of each diene rubber (weighted average value of glass transition temperature). The total weight fraction of all diene rubbers is 1.

  The rubber composition for a tire tread of the present invention can improve wet performance while blending a liquid resin at room temperature while maintaining the softness of the rubber at a low temperature and ensuring the performance on ice. Here, room temperature means 20 ° C.

The resin that is liquid at room temperature is composed of an adduct of camphene and a phenol compound. Camphene is a hydrocarbon represented by the following general formula (I).

  Resin that is liquid at room temperature comprising an adduct of camphene and a phenol compound has a glass transition temperature (Tg) of -10 ° C to 10 ° C, more preferably -10 ° C to 0 ° C. By setting the Tg of the liquid resin at room temperature within such a range, the wet performance can be improved while maintaining the softness of the rubber at a low temperature and ensuring the performance on ice. In general, when a resin having a Tg higher than that of the diene rubber is blended, the Tg of the entire rubber composition is increased, and the rubber hardness at a low temperature is increased, and there is a concern that the performance on ice is lowered. However, a liquid resin composed of an adduct of camphene and a phenol compound can unexpectedly improve wet performance and maintain performance on ice at a high level. The reason is that the phenol unit has the effect of improving the dispersibility of silica, and the camphene structure is appropriately compatible with the diene rubber containing NR · BR, thereby improving the flexibility of the rubber composition. it is conceivable that. As a result, even when a liquid resin composed of an adduct of camphene and a phenol compound is blended, an increase in rubber hardness at a low temperature can be suppressed despite having a relatively high Tg. Therefore, wet performance can be improved while ensuring excellent performance on ice. In addition, Tg of resin liquid at room temperature can be measured by the method mentioned above. The glass transition temperature of the resin that is liquid at room temperature is measured in the same manner as the diene rubber described above.

  The compounding amount of the resin which is liquid at room temperature is 1 to 10 parts by weight, more preferably 2 to 8 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the liquid resin at room temperature is less than 1 part by weight, the wet performance cannot be sufficiently improved. Moreover, when the compounding quantity of liquid resin at room temperature exceeds 10 weight part, there exists a possibility that performance on ice may fall. In addition, resin liquid at room temperature can be mix | blended so that a part of oil component normally mix | blended with a rubber composition may be substituted.

  The method for producing a resin that is liquid at room temperature is not particularly limited. For example, 0.1 to 6 mol, preferably 0.5 to 4 mol of a phenol compound is used per mol of camphene, and 20 to 20 mol in the presence of an acidic catalyst. It is obtained by reacting at a temperature of 150 ° C. for 1 to 10 hours. Examples of the acidic catalyst include hydrochloric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boron trifluoride or a complex thereof, a cation exchange resin, a heteropolyacid, and activated clay. At that time, a reaction solvent may not be used, but solvents such as aromatic hydrocarbons, alcohols, ethers and the like can also be used. Examples of the phenol compound include phenol, cresol, xylenol, propylphenol, nonylphenol, hydroquinone, resorcin, methoxyphenol, bromophenol, bisphenol A, bisphenol F, and the like. Moreover, these phenol compounds can also be used independently and can also be used in mixture of 2 or more types.

  In the rubber composition for a tire tread of the present invention, 20 parts by weight or more of silica is blended with 100 parts by weight of the diene rubber. By compounding silica, the performance on the ice and the wet performance of the rubber composition can be further improved.

  The amount of silica is 20 parts by weight or more, preferably 20 to 80 parts by weight, and more preferably 40 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. When the amount of silica is less than 20 parts by weight, the performance on ice and the wet performance cannot be sufficiently improved.

  In this invention, a silane coupling agent can be mix | blended with a silica. By compounding the silane coupling agent, the dispersibility of silica in the diene rubber can be improved, and the on-ice performance and wet performance can be further enhanced.

  The blending amount of the silane coupling agent is preferably 3 to 15% by weight, more preferably 5 to 10% by weight based on the blending amount of silica. When the silane coupling agent is less than 3% by weight of the silica content, the dispersion of silica cannot be improved sufficiently. When the compounding amount of the silane coupling agent exceeds 15% by weight of the silica compounding amount, the silane coupling agents are condensed with each other, and a desired effect cannot be obtained.

  The type of the silane coupling agent is not particularly limited as long as it can be used for the rubber composition containing silica. For example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3- Sulfur-containing silane coupling agents such as (triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane can be exemplified. .

  The rubber composition for tire treads of the present invention is not compatible with a diene rubber, and a crosslinkable oligomer or polymer having a glass transition temperature of −50 ° C. or lower is 0.3 to 100 parts by weight of the diene rubber. 30-12 parts by weight and 0.1-12 parts by weight of three-dimensionally crosslinked fine particles having an average particle size of 0.5-50 μm can be blended.

  The crosslinkable oligomer or polymer is also used as a diene rubber. “Incompatible” means that the components constituting the diene rubber and the crosslinkable oligomer or polymer are incompatible with each other.

  Examples of the crosslinkable oligomer or polymer include polyether-based, polyester-based, polyolefin-based, polycarbonate-based, acrylic-based or plant-based polymers or copolymers thereof.

  In addition, crosslinkable oligomers or polymers have a hydroxyl group, a silane functional group, an isocyanate group, a (meth) acryloyl group, an allyl group, a carboxy group, an acid because the on-ice performance of the tire becomes better by crosslinking between molecules. It preferably has at least one reactive functional group selected from the group consisting of an anhydride group and an epoxy group.

  These reactive functional groups are preferably at least at the end of the main chain of the crosslinkable oligomer or polymer. When the main chain is linear, it is preferably 1.5 or more, more preferably 2 or more. It is good. On the other hand, when the main chain is branched, it is preferably 3 or more.

  The weight average molecular weight or number average molecular weight of the crosslinkable oligomer or polymer is preferably 300 to 30000, more preferably 500 to 25000, and the dispersibility in the diene rubber and the kneading processability of the rubber composition are improved. In the cross-linkable oligomer or polymer, it is easy to adjust the particle size and shape when preparing the fine particles described later. Here, the weight average molecular weight and the number average molecular weight are both measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  The crosslinkable oligomer or polymer preferably has a glass transition temperature of −50 ° C. or lower, more preferably −100 ° C. to −50 ° C., and still more preferably −90 ° C. to −60 ° C. When the glass transition temperature of the crosslinkable oligomer or polymer is higher than −50 ° C., the performance on ice may be deteriorated. The glass transition temperature of the crosslinkable oligomer or polymer is measured in the same manner as the diene rubber described above.

  Furthermore, the compounding amount of the crosslinkable oligomer or polymer is preferably 0.3 to 30 parts by weight, more preferably 0.5 to 25 parts by weight, still more preferably 1 to 15 parts by weight with respect to 100 parts by weight of the diene rubber. It is good to make it. If the amount of the crosslinkable oligomer or polymer is less than 0.3 parts by weight, the performance on ice cannot be improved sufficiently. Moreover, when the compounding quantity of a crosslinkable oligomer or polymer exceeds 30 weight part, wet performance will deteriorate.

  In the present invention, the fine particles suitably blended with the crosslinkable oligomer or polymer are fine particles having a three-dimensionally crosslinked average particle size of 0.5 to 50 μm. The average particle diameter is preferably 1 to 50 μm, more preferably 5 to 40 μm, and the surface of the tire becomes moderately rough and the performance on ice becomes better. Here, the average particle diameter means an average value of equivalent circle diameters measured using a laser microscope. For example, a laser diffraction scattering type particle size distribution measuring apparatus LA-300 (manufactured by Horiba, Ltd.), a laser microscope VK-8710. (Manufactured by Keyence Corporation).

  The compounding amount of the three-dimensionally crosslinked fine particles is preferably 0.1 to 12 parts by weight, more preferably 0.3 to 10 parts by weight, still more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the diene rubber. There should be. By blending the three-dimensionally crosslinked fine particles within such a range, the on-ice performance and the wear resistance of the rubber composition for a tire tread are improved.

  The three-dimensionally crosslinked fine particles are preferably fine particles obtained by three-dimensionally cross-linking oligomers or polymers that are not compatible with the crosslinkable oligomers or polymers in advance. Thereby, the on-ice performance and the wear resistance of the tire become better. Therefore, the cross-linkable oligomer or polymer functions as a solvent when preparing three-dimensionally cross-linked fine particles, and the cross-linkable oligomer or polymer and three-dimensional cross-linked fine particles are used when blending these mixtures into the rubber composition. The dispersibility of can be improved.

  Examples of the three-dimensionally crosslinked fine particles include fine particles formed of a polycarbonate-based, aliphatic-based, saturated hydrocarbon-based, acrylic-based or plant-derived polymer or copolymer. Of these, those formed from aliphatic polymers or copolymers are preferred, and liquid diene polymers are more preferred. Examples of the liquid diene-based polymer include liquid polyisoprene and liquid polybutadiene, and the on-ice performance and wear resistance of the tire become better.

  The three-dimensionally crosslinked fine particles preferably have other reactive functional groups that are different from the reactive functional groups of the crosslinkable oligomer or polymer and do not react with these. As the other reactive functional group, at least one or more is selected from the group consisting of a hydroxyl group, a silane functional group, an isocyanate group, a (meth) acryloyl group, an allyl group, a carboxy group, an acid anhydride group, and an epoxy group. Here, the silane functional group is also called a so-called crosslinkable silyl group, for example, a hydrolyzable silyl group; a silanol group; a functional group in which the silanol group is substituted with an acetoxy group derivative, an enoxy group derivative, an oxime group derivative, an amine derivative, or the like. Groups and the like.

  The weight average molecular weight or number average molecular weight of the three-dimensionally crosslinked fine particles is not particularly limited, but is preferably 1000 to 100,000, and more preferably 3000 to 60000. Thereby, the particle diameter and the crosslinking density become appropriate, and the performance on ice of the tire becomes better. Here, both weight average molecular weight or number average molecular weight shall be measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  Examples of the method of preparing the three-dimensionally crosslinked fine particles in the crosslinkable oligomer or polymer include a method of three-dimensional crosslinking using a reactive functional group of the constituent material of the fine particles. Specifically, at least one component selected from the group consisting of a constituent material having another reactive functional group described above and a compound having a functional group that reacts with water, a catalyst, and another reactive functional group. The method of making it react and carrying out three-dimensional crosslinking etc. are mentioned. At this time, it is preferable to prepare using additives, such as surfactant, an emulsifier, a dispersing agent, a silane coupling agent.

  The rubber composition for a tire tread of the present invention can contain 0.2 to 30 parts by weight of thermally expandable microcapsules with respect to 100 parts by weight of diene rubber. The performance on ice can be further improved by blending the thermally expandable microcapsules.

  The amount of the thermally expandable microcapsule is preferably 0.5 to 25 parts by weight, more preferably 1 to 20 parts by weight with respect to 100 parts by weight of the diene rubber. When the amount of the thermally expandable microcapsule is less than 0.2 parts by weight, the volume of the hollow particles (microcapsule shell) in which the thermally expandable microcapsule expanded during vulcanization is insufficient, and the performance on ice is sufficiently improved. I can't. Moreover, when the compounding quantity of a thermally expansible microcapsule exceeds 30 weight part, there exists a possibility that the abrasion resistance performance of a rubber composition may deteriorate.

  The thermally expandable microcapsule has a configuration in which a thermally expandable substance is encapsulated in a shell formed of a thermoplastic resin. For this reason, when vulcanizing and molding an unvulcanized tire, if the microcapsules dispersed in the rubber composition are heated, the thermally expandable substance contained in the shell material expands to increase the particle size of the shell material. A large number of hollow particles are formed in the tread rubber. As a result, the water film generated on the surface of the ice is efficiently absorbed and removed, and a micro edge effect is obtained, thereby improving the performance on ice. In addition, since the shell material of the microcapsule is harder than the tread rubber, the wear resistance of the tread portion can be increased. The shell material of the thermally expandable microcapsule can be formed of a nitrile polymer.

  Moreover, the thermally expansible substance included in the shell material of the microcapsule has a property of being vaporized or expanded by heat, and examples thereof include at least one selected from the group consisting of hydrocarbons such as normal alkane and isoalkane. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, and examples of normal alkanes include n-butane, n-propane, n-hexane, Examples thereof include n-heptane and n-octane. These hydrocarbons may be used alone or in combination. As a preferable form of the thermally expandable substance, a substance obtained by dissolving a hydrocarbon which is gaseous at normal temperature in a hydrocarbon which is liquid at normal temperature is preferable. By using such a mixture of hydrocarbons, a sufficient expansion force can be obtained from the low temperature region to the high temperature region in the vulcanization molding temperature region (150 to 190 ° C.) of the unvulcanized tire.

  The rubber composition for tire tread can mix | blend fillers other than a silica. Examples of other fillers include carbon black, talc, clay, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, titanium oxide, calcium sulfate, and mica. Of these, carbon black is preferred. By blending other fillers, the strength of the rubber can be increased and the wear resistance can be improved. The blending amount of the other filler is preferably 4 to 80 parts by weight, more preferably 10 to 60 parts by weight with respect to 100 parts by weight of the diene rubber.

  In addition to the fillers described above, tire rubber compositions for tire tread are generally used for tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, etc. Various additives can be blended. Such an additive can be kneaded by a general method to form an unvulcanized rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. Such a rubber composition can be produced by mixing each of the above components using a known rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like.

  The rubber composition for a tire tread of the present invention is suitable for constituting a tread portion of a studless tire. The tread portion configured as described above can improve the performance on ice and the wet performance to a level higher than the conventional level.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

Synthesis Example 1 (Preparation of adduct of camphene and phenol compound)
Into a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel and a condenser tube was charged 188 g of phenol (2 mol) and 4 g of a strongly acidic cation exchange resin, and then maintained at a temperature of 100 ° C., 272 g of camphene ( 2 mol) was added dropwise over 3 hours, followed by stirring for 3 hours for reaction. Subsequently, the cation exchange resin was removed from the mixed solution by filtration, and the obtained reaction solution was distilled under a reduced pressure of 10 mmHg to obtain 360 g of a fraction having a boiling point of 145 ° C. to 155 ° C. The obtained fraction had a number average molecular weight (Mn) of 230 and a glass transition point of −6 ° C.

  20 types of rubber compositions (standard examples, Examples 1 to 9, Comparative Examples 1 to 10) composed of the compounding agents shown in Tables 1 and 2 are used as a common compounding agent shown in Table 3, sulfur, and a vulcanization accelerator. In addition, the components excluding the heat-expandable microcapsules are kneaded for 5 minutes with a 1.8 L closed mixer, discharged and cooled, and added with sulfur, a vulcanization accelerator, and the heat-expandable microcapsules and mixed with an open roll. It was prepared by. In addition, the compounding quantity of each compounding agent described in Table 3 was shown by the weight part with respect to 100 weight part of diene rubber described in Table 1,2. The compounding amount of the crosslinkable polymer containing the three-dimensionally crosslinked fine particles is described in the column of “fine particle-containing crosslinkable polymer” in Tables 1 and 2, and the amount of the three-dimensionally crosslinked fine particles is described in parentheses at the bottom. Tables 1 and 2 show the average glass transition temperatures (Tg) of the diene rubbers contained in the rubber compositions of Examples and Comparative Examples.

  Twenty kinds of obtained rubber compositions were press vulcanized in a predetermined mold at 170 ° C. for 10 minutes to prepare vulcanized rubber test pieces made of a tire tread rubber composition. The performance on ice of the obtained vulcanized rubber test piece was evaluated by the method shown below.

On-ice performance The obtained vulcanized rubber test piece was affixed to a flat columnar base rubber and measured using an inside drum type on-ice friction tester at a measurement temperature of -1.5 ° C, a load of 5.5 kg / cm ³ , and a drum rotation. The friction coefficient on ice was measured at a speed of 25 km / h. The obtained coefficient of friction on ice was shown in the column of “performance on ice” in Tables 1 and 2 as an index with the value of the standard example as 100. A larger index value means a greater frictional force on ice and better performance on ice.

Wet performance The dynamic viscoelasticity of the obtained vulcanized rubber test piece was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz. Tan δ was calculated. The obtained results are expressed as an index with the value of the standard example being 100, and are shown in the “Wet performance” column of Tables 1 and 2. A larger index means better wet braking performance.

In Tables 1 and 2, the types of raw materials used are shown below.
・ NR: Natural rubber, RSS # 3
BR: Butadiene rubber, Nippon Zeon BR1220
SBR: styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon
・ Carbon black: Seast KH manufactured by Tokai Carbon Co., Ltd.
Silica: Nippon Sil AQ manufactured by Nippon Silica
Coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Degussa
Resin component 1: A terpene resin which is liquid at room temperature and is composed of an adduct of camphene and a phenol compound produced in Synthesis Example 1, has a glass transition temperature (Tg) of −6.0 ° C.
Resin component 2: liquid terpene resin at room temperature, Tg of −53 ° C., YS resin PX200 manufactured by Yashara Chemical Co., Ltd.
Resin component 3: Terpene resin that is liquid at room temperature, Tg is −38 ° C., Dimaron manufactured by Yashara Chemical Co., Ltd. Resin component 4: Coumarone indene resin that is liquid at room temperature, Tg is −13 ° C., NOVARES C30 manufactured by RUTGERS
Resin component 5: terpene resin that is solid at room temperature, Tg of 30 ° C., YS resin PX800 manufactured by Yasuhara Chemical
-Microcapsule: Matsumoto Yushi Seiyaku Co., Ltd. Matsumoto Yushi Seiyaku Co., Ltd. thermally expandable microcapsule (Microsphere F100)
Aroma oil: Showa Shell Sekiyu Extract 4S
Fine particle-containing crosslinkable polymer: a crosslinkable polymer containing three-dimensionally crosslinked fine particles obtained by the following preparation method

<Preparation of fine particle-containing crosslinkable polymer>
200 g of maleic acid-modified liquid polyisoprene rubber (Kuraprene LIR-403, number average molecular weight: 34000, manufactured by Kuraray Co., Ltd.), 120 g of process oil (Diana Process Oil PS-32, manufactured by Idemitsu Kosan Co., Ltd.), oxazolidine compound (Hardener OZ, 16 g of Sumika Bayer Urethane Co., Ltd., 1600 g of hydrolyzable silyl group-terminated polyoxypropylene glycol (MS polymer S810, Kaneka Corp.), and 5 g of water, with a concentric twin screw mixer (Inoue Seisakusho Co., Ltd.) The mixture was stirred for 1 hour at a low speed of 36 rpm and a high speed disper of 600 rpm.

  Next, 6 g of a pluronic type nonionic surfactant (New Pole PE-64, manufactured by Sanyo Chemical Industries) and 6 g of aminosilane (A1110, manufactured by Nihon Unicar) are added thereto, and further, a low speed of 36 rpm and a high speed disperser are added. A paste-like product was prepared by stirring at 2000 rpm for 30 minutes.

  When this pasty product is observed using a laser microscope VK-8710 (manufactured by Keyence Corporation), fine particles (skeleton: polyisoprene, cross-linking: amide ester bond) having a particle diameter of 0.5 to 10 μm are formed, and water is added. It was confirmed that it was dispersed in the decomposable silyl group-terminated polyoxypropylene glycol. Further, as a result of image processing and 3D profiling of this image, the content (% by mass) of fine particles in the pasty product was about 11%.

In Table 3, the types of raw materials used are shown below.
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Bead stearic acid manufactured by NOF Corporation-Anti-aging agent 1: Santoflex 6PPD manufactured by Flexsys
Anti-aging agent 2: Nocrack 224 manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. ・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical

  As is clear from Table 1, it was confirmed that the rubber compositions for tire treads of Examples 1 to 9 improved the performance on ice and the wet performance to the conventional level or more.

  Since the rubber composition of Comparative Example 1 did not contain a liquid resin at room temperature, the wet performance was inferior. The rubber composition of Comparative Example 2 has poor performance on ice because the Tg of the diene rubber is higher than −60 ° C. The rubber composition of Comparative Example 3 has inferior performance on ice because the compounding amount of silica is less than 20 parts by weight.

  In the rubber compositions of Comparative Examples 4 and 5-6, the resin components 2 and 3 are not adducts of camphene and a phenol compound, and their Tg is lower than −10 ° C., so that the wet performance is inferior. The rubber compositions of Comparative Examples 7 and 8 have poor performance on ice because the resin component 4 is not an adduct of camphene and a phenol compound.

  In the rubber composition of Comparative Example 9, since the resin component 5 is not an adduct of camphene and a phenol compound, and its Tg is higher than 10 ° C., the performance on ice is inferior. Since the compounding quantity of the resin component 1 exceeds 10 weight part, the performance on ice of the rubber composition of the comparative example 10 is inferior.

Claims (4)

  A rubber composition comprising 20 parts by weight or more of silica and 1 to 10 parts by weight of a liquid resin at room temperature in 100 parts by weight of a diene rubber, wherein the diene rubber contains natural rubber and butadiene rubber, An average glass transition temperature is −60 ° C. or lower, and the resin that is liquid at room temperature is an adduct of camphene and a phenol compound, and its glass transition temperature is −10 ° C. to 10 ° C. Rubber composition.   While blending 100 to 30 parts by weight of the diene rubber with 0.1 to 30 parts by weight of a crosslinkable oligomer or polymer and 0.1 to 12 parts by weight of three-dimensionally crosslinked fine particles having an average particle size of 0.5 to 50 μm. The rubber composition for a tire tread according to claim 1, wherein the crosslinkable oligomer or polymer is incompatible with the diene rubber and has a glass transition temperature of -50 ° C or lower.   The rubber composition for a tire tread according to claim 1 or 2, wherein 0.2 to 30 parts by weight of thermally expandable microcapsules is blended with 100 parts by weight of the diene rubber.   The studless tire which formed the tread part with the rubber composition for tire treads in any one of Claims 1-3.